Rollup merge of #86843 - FabianWolff:issue-86820, r=lcnr

Check that const parameters of trait methods have compatible types

This PR fixes #86820. The problem is that this currently passes the type checker:
```rust
trait Tr {
    fn foo<const N: u8>(self) -> u8;
}

impl Tr for f32 {
    fn foo<const N: bool>(self) -> u8 { 42 }
}
```
i.e. the type checker fails to check whether const parameters in `impl` methods have the same type as the corresponding declaration in the trait. With my changes, I get, for the above code:
```
error[E0053]: method `foo` has an incompatible const parameter type for trait
 --> test.rs:6:18
  |
6 |     fn foo<const N: bool>(self) -> u8 { 42 }
  |                  ^
  |
note: the const parameter `N` has type `bool`, but the declaration in trait `Tr::foo` has type `u8`
 --> test.rs:2:18
  |
2 |     fn foo<const N: u8>(self) -> u8;
  |                  ^

error: aborting due to previous error
```
This fixes #86820, where an ICE happens later on because the trait method is declared with a const parameter of type `u8`, but the `impl` uses one of type `usize`:
> `expected int of size 8, but got size 1`

src/test/ui/const-generics/issue-86820.rs

@@ -0,0 +1,25 @@
+// Regression test for the ICE described in #86820.
+
+#![allow(unused,dead_code)]
+use std::ops::BitAnd;
+
+const C: fn() = || is_set();
+fn is_set() {
+    0xffu8.bit::<0>();
+}
+
+trait Bits {
+    fn bit<const I : u8>(self) -> bool;
+    //~^ NOTE: the const parameter `I` has type `usize`, but the declaration in trait `Bits::bit` has type `u8`
+}
+
+impl Bits for u8 {
+    fn bit<const I : usize>(self) -> bool {
+    //~^ ERROR: method `bit` has an incompatible const parameter type for trait [E0053]
+        let i = 1 << I;
+        let mask = u8::from(i);
+        mask & self == mask
+    }
+}
+
+fn main() {}

src/test/ui/const-generics/issue-86820.stderr

@@ -0,0 +1,15 @@
+error[E0053]: method `bit` has an incompatible const parameter type for trait
+  --> $DIR/issue-86820.rs:17:18
+   |
+LL |     fn bit<const I : usize>(self) -> bool {
+   |                  ^
+   |
+note: the const parameter `I` has type `usize`, but the declaration in trait `Bits::bit` has type `u8`
+  --> $DIR/issue-86820.rs:12:18
+   |
+LL |     fn bit<const I : u8>(self) -> bool;
+   |                  ^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0053`.